Etch damage repair with thermal annealing

ABSTRACT

A method of manufacturing a semiconductor device etches a feature on a substrate in accordance with a photoresist mask. The photoresist mask is removed by plasma etching. Laser thermal annealing is performed to vaporize polymer residue created during the stripping of the photoresist mask, and to repair damage to the substrate.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor processing,and more particularly, to repairinig the etch damage created duringsemiconductor processing.

BACKGROUND OF THE INVENTION

Over the last few decades, the semiconductor industry has undergone arevolution by the use of semiconductor technology to fabricate small,highly integrated electronic devices, and the most common semiconductortechnology presently used is silicon-based. A large variety ofsemiconductor devices have been manufactured having various applicationsin numerous disciplines. One silicon-based semiconductor device is ametal-oxide-semiconductor (MOS) transistor. The MOS transistor is one ofthe basic building blocks of most modern electronic circuits.Importantly, these electronic circuits realized improved performance andlower costs, as the performance of the MOS transistors increased and asmanufacturing costs are reduced.

A typical MOS semiconductor device includes a semiconductor substrate onwhich a gate electrode is formed over a gate dielectric. The gateelectrode, which acts as a conductor, receives an input signal tocontrol operation of the device. Source and drain regions are typicallyformed in regions of the substrate adjacent the gate electrodes bydoping the regions with a dopant of a desired conductivity. Theconductivity of the doped region depends on the type of impurity used todope the region. The typical MOS transistor is symmetrical, in that thesource and drain are interchangeable. Whether a region acts as a sourceor drain typically depends on the respective applied voltages and thetype of device being made. The collective term source/drain region isused herein to generally describe an active region used for theformation of either a source or drain.

In creating the MOS transistor or other semiconductor device, theprocess typically involves a plasma etch process to etch material toform structures. For example, a silicon substrate may have a gate oxidelayer or other layer serving as an etch stop layer provided on the topof the silicon substrate. A gate electrode layer, such as polysilicon,is provided on the oxide. A photoresist mask material is deposited andpatterned by known photolithography techniques. The plasma etch processis then performed to remove portions of the gate layer that are notprotected by the patterned photoresist mask.

After the plasma etch is performed, stopping on the etch stop layer,such as a gate oxide, a gate electrode has been created. The plasmaetch, however, damages the etch stop layer and the underlying layers,such as the silicon substrate. The photoresist is rapidly removed in aresist strip process, and pre-diffusion or pre-rapid thermal anneal(RTA) wet cleans are done to remove polymer residue and photoresist. Thepolymer residue and photoresist must be removed before the damage can berepaired by the thermal anneal process.

The damage to the substrate caused by exposure to the plasma results inthe enhanced oxidation of the silicon substrate in subsequentoxidations. The thicker oxide that is formed on the substrate operatesto undesirably screen subsequent source/drain implants due to the damagedone to the substrate by plasma.

There is a need for an improved process to repair the damage caused toetch stop layers and underlying substrates following a plasma etchprocess.

SUMMARY OF THE INVENTION

This and other needs are met by embodiments of the present inventionswhich provide a method of manufacturing a semiconductor device,comprising the steps of etching a feature on a substrate in accordancewith a photoresist mask and stripping the photoresist mask by plasmaremoval. The substrate is laser thermal annealed to repair damage to thesubstrate.

By the use of laser thermal annealing, following the plasma etch, thepolymer residue left over from the stripping of the resist is vaporizedby the laser thermal annealing process. Further, the laser thermalannealing repairs the damage to the etch stop layer and underlyinglayers. This prevents the growth of thick oxide on the previouslydamaged substrate, thereby avoiding screening during subsequentsource/drain implantation steps.

The other stated needs are also met by other embodiments of the presentinvention which provide a method of forming semiconductor devicecomprising the steps of forming an etch stop layer on a substrate andforming a gate layer on the etch stop layer. A photoresist mask iscreated on the gate layer. This gate layer is etched in accordance withthe photoresist mask by plasma etching. The photoresist mask itself isremoved by plasma etching. Laser thermal annealing is performed to theetch stop layer and the substrate.

The foregoing and other features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic depiction of a semiconductordevice during one processing step in accordance with embodiments of thepresent invention.

FIG. 2 depicts the structure of FIG. 1 following the deposition andpatterning of a photoresist mask layer in accordance with embodiments ofthe present invention.

FIG. 3 shows the structure of FIG. 2 following the plasma etching of thegate layer in accordance with embodiments of the present invention.

FIG. 4 depicts the structure of FIG. 3 following a plasma etch strip ofthe photoresist mask material, leaving a residue, in accordance withembodiments of the present invention.

FIG. 5 shows the structure of FIG. 4 during a laser thermal annealingprocess, in accordance with embodiments of the present invention.

FIG. 6 depicts the structure of FIG. 5 following the shallowimplantation of dopants into the repaired substrate, in accordance withembodiments of the present invention.

FIG. 7 shows the structure of FIG. 6 following the formation of sidewallspacers and deep implantation of dopants to create source/drain regionsin the substrate, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses and solves problems related to theetching of features of the semiconductor device by plasma etching. Theseproblems include damage to the etch stop layers and to underlyingsubstrates caused by the plasma etching process. The present inventionprovides for removal of the photoresist by plasma removal after theplasma etch process has been completed. Any polymer residues left afterthe plasma resist stripping are removed by laser thermal annealing. Thislaser thermal annealing is performed at an energy level sufficient tovaporize the polymer residues. At the same time, the laser thermalannealing repairs the damage to the etch stop layer and the underlyinglayers caused by the plasma etching.

FIG. 1 is a schematic cross-sectional depiction of a portion of asemiconductor device during one step of its formation. In the depictedembodiment, a silicon substrate 10 is provided upon which a gatedielectric layer 12, such as a gate oxide, has been provided. The gateoxide may be formed by thermal oxidation, for example, or othertechnique. As will become apparent in the following description, thegate dielectric layer 12 may also be considered to be an etch stoplayer, and will be referred to as such during portions of thisdescription. Also, the gate dielectric layer 12 and the siliconsubstrate 10 may be considered in combination as a substrate foroverlying layers.

An overlying layer 14, such as a polysilicon layer, is provided on asubstrate comprising the gate oxide of the gate dielectric layer 12 andthe silicon substrate layer 10. This polysilicon layer 14 may beconsidered a gate layer, since the polysilicon layer 14 will be etchedto form a gate electrode. The polysilicon layer 14 may be deposited byany conventional methodology to a desired thickness.

FIG. 2 shows the structure of FIG. 1 following the depositing andpatterning of a photoresist mask 16. The gate electrode will be definedby the pattern of the photoresist mask 16. Conventional methods offorming the photoresist mask 16 may be employed in the presentinvention.

In FIG. 3, a plasma etch process, which is an anisotrophic etch, hasbeen employed to etch the polysilicon of the polysilicon layer 14. Thephotoresist mask 16 protects the underlying polysilicon in a polysiliconlayer 14. A plasma etch process, which may be any conventional plasmaetch process known to those of ordinary skill in the art suitable foretching the material in the particular layer and stopping on theunderlying layer, may be employed. A typical plasma etch of polysiliconmay be any number of different plasma chemistries. For example,HBr/Cl₂O₂ exhibits increased selectivity to silicon dioxide andphotoresist in comparison to other etch chemistries. However, in otherembodiments, other etch chemistries may be employed without departingfrom the scope of the invention. Furthermore, different etchants mayused in dependence upon the overlying layer 14 and the underlying layers10, 12, as the invention is not limited to the particular materialsemployed.

FIG. 3 shows the results of the plasma etch that has been performed, tocreate the gate electrode 18. The damage regions 20 are indicated. Thedamage is created by the plasma etch process. Such damage has beentypically repaired by rapid thermal annealing following the rapidremoval of the photoresist 16 and pre-diffusion or pre-RTA wet cleansthat must be done to remove the polymer and the photoresist 16 prior tothe rapid thermal annealing. Such steps, in the prior art, increasedmanufacturing costs and processing steps in the semiconductormanufacturing process.

In FIG. 4, the plasma has been employed to strip the resist 16 from thegate electrode 18. However, this has the effect of creating residue 22.This residue 22 needs to be removed prior to the repairing of the damageto the oxide layer 12 and the substrate layer 10. Removal of polymerresidue 22 normally requires an aggressive cleaning step.

In the present invention, laser thermal annealing is performed to bothremove the polymer residues 22 and to repair the damage caused to thegate oxide 12 and the substrate layer 10. The single step process avoidsthe extra steps employed in conventional techniques to remove theresidues by pre-diffusion or pre-RTA wet cleans performed prior to rapidthermal annealing. The laser thermal etching process vaporizes thepolymer residues 22 at the same time it repairs the damage to the etchstop layer formed by the gate oxide 12 and the damage to the underlyingsilicon substrate layer 10.

During the laser thermal annealing, the results of which are depicted inFIG. 5, the substrate, formed by the silicon substrate layer 10 and the,oxide layer 12, receives the energy from a laser (not shown). An exampleof a laser capable of providing this energy is a spatially homogenized308 nm XeCl pulsed laser. However, the invention is not limited in thismanner, and the energy and power of the laser can vary in accordancewith different applications. Although not limited in this manner, anexemplary fluence range for laser irradiation can extend from betweenabout 1 mJ/cm² to about 1.3 J/cm².

Hence, the present invention acts to vaporize the polymer residues 22and remove them from the surfaces of the gate electrode 18 and the etchstop layer formed by the gate oxide layer 12 and the gate electrode 18.At the same time, the silicon substrate layer 10 and the gate oxidelayer 12 are repaired by the damage caused by the plasma etch processperformed earlier. This simultaneous cleaning of residue and repairingof etch damage prevents the use of two separate steps to achieve thesegoals.

Following the laser thermal annealing, shallow implants into therepaired silicon substrate layer 10 are provided to create shallowimplant regions 24, as shown in FIG. 6. Conventional dopants and ionimplant energy levels may be employed, for example, to create theshallow implant regions 24.

FIG. 7 shows the structure of FIG. 6 after sidewall spacers 26 have beenformed on the sides of the gate electrode 18, and deep implants havebeen made into the silicon substrate layer 10 to create source/drainregions 28.

One of the advantages of the invention is that the silicon substrate 10is prevented from growing thicker oxide that can screen the source/drainimplants. Using laser thermal annealing to repair the damage avoids theundesirable growth of thick oxide on the substrate 10.

Although the present invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the scope of the present invention being limited only by theterms of the appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising the steps of: etching a feature on a substrate in accordancewith a photoresist mask; stripping the photoresist mask by plasmaremoval; and laser thermal annealing the substrate to repair damage tothe substrate.
 2. The method of claim 1, wherein the step of laserthermal annealing is performed at an energy level sufficient to vaporizepolymer residue created during stripping of the photoresist mask.
 3. Themethod of claim 2, wherein the substrate comprises a silicon substratelayer and an etch stop layer on the silicon substrate layer.
 4. Themethod of claim 3, wherein the etch stop layer is an oxide layer.
 5. Themethod of claim 4, wherein the laser thermal annealing is performed witha fluence range for laser irradiation between about 1 mJ/cm² to about1.3 J/cm².
 6. The method of claim 5, wherein the feature is a gateelectrode.
 7. The method of claim 6, wherein the step of etching afeature includes plasma etching a layer to form the feature.
 8. A methodof forming a semiconductor device, comprising the steps of: forming anetch stop layer on a substrate; forming a gate layer on the etch stoplayer; creating a photoresist mask on the gate layer; etching the gatelayer in accordance with the photoresist mask by plasma etching;removing the photoresist mask by plasma etching; and laser thermalannealing the etch stop layer and the substrate.
 9. The method of claim8, wherein the plasma etching creates damage in the etch stop layer andthe substrate, and wherein the laser thermal annealing is performed atan energy level sufficient to repair the damage in the etch stop layerand the substrate.
 10. The method of claim 9, wherein the laser thermalannealing is performed with a fluence range for laser irradiationbetween about 1 mJ/cm² to about 1.3 J/cm².
 11. The method of claim 9,wherein removing the photoresist mask creates polymer residue andwherein the laser thermal annealing is performed at an energy levelsufficient to vaporize the polymer residue.